Full-Length Venom Protein cDNA Sequences from Venom-Derived mRNA: Exploring Compositional Variation and Adaptive Multigene Evolution

Envenomation of humans by snakes is a complex and continuously evolving medical emergency, and treatment is made that much more difficult by the diverse biochemical composition of many venoms. Venomous snakes and their venoms also provide models for the study of molecular evolutionary processes leading to adaptation and genotype-phenotype relationships. To compare venom complexity and protein sequences, venom gland transcriptomes are assembled, which usually requires the sacrifice of snakes for tissue. However, toxin transcripts are also present in venoms, offering the possibility of obtaining cDNA sequences directly from venom. This study provides evidence that unknown full-length venom protein transcripts can be obtained from the venoms of multiple species from all major venomous snake families. These unknown venom protein cDNAs are obtained by the use of primers designed from conserved signal peptide sequences within each venom protein superfamily. This technique was used to assemble a partial venom gland transcriptome for the Middle American Rattlesnake (Crotalus simus tzabcan) by amplifying sequences for phospholipases A₂, serine proteases, C-lectins, and metalloproteinases from within venom. Phospholipase A₂ sequences were also recovered from the venoms of several rattlesnakes and an elapid snake (Pseudechis porphyriacus), and three-finger toxin sequences were recovered from multiple rear-fanged snake species, demonstrating that the three major clades of advanced snakes (Elapidae, Viperidae, Colubridae) have stable mRNA present in their venoms. These cDNA sequences from venom were then used to explore potential activities derived from protein sequence similarities and evolutionary histories within these large multigene superfamilies. Venom-derived sequences can also be used to aid in characterizing venoms that lack proteomic profiles and identify sequence characteristics indicating specific envenomation profiles. This approach, requiring only venom, provides access to cDNA sequences in the absence of living specimens, even from commercial venom sources, to evaluate important regional differences in venom composition and to study snake venom protein evolution.

This work demonstrates that full-length venom protein messenger RNAs are present in secreted venoms and can be used to acquire full-length protein sequences of toxins from both front-fanged (Elapidae, Viperidae) and rear-fanged (Colubridae) snake venoms, eliminating the need to use venom glands. Full-length transcripts were obtained from venom samples that were fresh, newly lyophilized, old, field desiccated or commercially prepared, representing a significant advance over previous attempts which produced only partial sequence transcripts. Transcripts for all major venom protein families (metalloproteinases, serine proteases, C-type lectins, phospholipases A₂ and three-finger toxins) responsible for clinically significant snakebite symptoms were obtained from venoms. These sequences aid in the identification and characterization of venom proteome profiles, allowing for the identification of peptide sequences, specific isoforms, and novel venom proteins. The application of this technique will help to provide venom protein sequences for many snake species, including understudied rear-fanged snakes. Venom protein transcripts offer important insights into potential snakebite envenomation profiles and the molecular evolution of venom protein multigene families. By requiring only venom to obtain venom protein cDNAs, the approach detailed here will provide access to cDNA-based protein sequences from commercial and other venom sources, facilitating study of snake venom protein composition and evolution.

Venom proteomes of South and North American opisthoglyphous (Colubridae and Dipsadidae) snake species: a preliminary approach to understanding their biological roles

Opisthoglyphous snake venoms remain under-explored despite being promising sources for ecological, evolutionary and biomedical/biotechnological research. Herein, we compared the protein composition and enzymatic properties of the venoms of Philodryas baroni (PbV), Philodryas olfersii olfersii (PooV) and Philodryas patagoniensis (PpV) from South America, and Hypsiglena torquata texana (HttV) and Trimorphodon biscutatus lambda (TblV) from North America. All venoms degraded azocasein, and this metalloproteinase activity was significantly inhibited by EDTA. PooV exhibited the highest level of catalytic activity towards synthetic substrates for serine proteinases. All venoms hydrolyzed acetylthiocholine at low levels, and only TblV showed phospholipase A(2) activity. 1D and 2D SDS-PAGE profile comparisons demonstrated species-specific components as well as several shared components. Size exclusion chromatograms from the three Philodryas venoms and HttV were similar, but TblV showed a notably different pattern. MALDI-TOF MS of crude venoms revealed as many as 49 distinct protein masses, assigned to six protein families. MALDI-TOF/TOF MS analysis of tryptic peptides confirmed the presence of cysteine-rich secretory proteins in all venoms, as well as a phospholipase A(2) and a three-finger toxin in TblV. Broad patterns of protein composition appear to follow phylogenetic lines, with finer scale variation likely influenced by ecological factors such as diet and habitat.

Duvernoy's gland secretion of Philodryas olfersii and Philodryas patagoniensis (Colubridae): Neutralization of local and systemic effects by commercial bothropic antivenom (Bothrops genus)

Colubrids involved in human envenomation in Brazil are mainly from the genera Helicops, Oxyrhopus, Thamnodynastes and Philodryas. There is a relatively large number of clinical descriptions involving the Xenodontinae snakes, Philodryas olfersii and Philodryas patagoniensis, in human accidents. The most common manifestations of envenomation are local pain, swelling, erythema and ecchymosis and regional lymphadenopathy with normal coagulation. The aims of this study were to characterize the biochemical and biological properties of P. olfersii and P. patagoniensis venoms, and to investigate their immunological cross-reactivities by using both specific antisera and anti-Bothrops sp serum used for human serum therapy in Brazil, in neutralizing the lethal and hemorrhagic effects of these venoms. We show here that P. olfersii e P. patagoniensis venoms present proteolytic and haemorrhagic activities but are devoid of phospholipase A2 activity. Haemorrhage and lethality induced by P. olfersii and P. patagoniensis are associated with metal-dependent proteinases, since EDTA could block these toxic activities. P. olfersii and P. patagoniensis venoms were immunogenic and the antisera produced were able to recognize several bands in P. olfersii, P. patagoniensis venoms in Bothrops jararaca venom.

Analysis of Colubroidea snake venoms by liquid chromatography with mass spectrometry: evolutionary and toxinological implications

The evolution of the venomous function of snakes and the diversification of the toxins has been of tremendous research interest and considerable debate. It has become recently evident that the evolution of the toxins in the advanced snakes (Colubroidea) predated the evolution of the advanced, front-fanged delivery mechanisms. Historically, the venoms of snakes lacking front-fanged venom-delivery systems (conventionally grouped into the paraphyletic family Colubridae) have been largely neglected. In this study we used liquid chromatography with mass spectrometry (LC/MS) to analyze a large number of venoms from a wide array of species representing the major advanced snake clades Atractaspididae, Colubrinae, Elapidae, Homalopsinae, Natricinae, Psammophiinae, Pseudoxyrhophiinae, Xenodontinae, and Viperidae. We also present the first sequences of toxins from Azemiops feae as well as additional toxin sequences from the Colubrinae. The large body of data on molecular masses and retention times thus assembled demonstrates a hitherto unsuspected diversity of toxins in all lineages, having implications ranging from clinical management of envenomings to venom evolution to the use of isolated toxins as leads for drug design and development. Although definitive assignment of a toxin to a protein family can only be done through demonstrated structural studies such as N-terminal sequencing, the molecular mass data complemented by LC retention information, presented here, do permit formulation of reasonable hypotheses concerning snake venom evolution and potential clinical effects to a degree not possible till now, and some hypotheses of this kind are proposed here. The data will also be useful in biodiscovery.